Ch 19,
Temperature

Thermometers and the Celsius Temperature Scale

The thermometer you most readily think of is probably a
liquid-in-glass thermometer like the one sketched here. Mercury or
colored alcohol is contained in a bulb at the base of a thin tube
of glass. The change in the length of the glass tube with
variation in temperature is so small that we can ignore that and
concentrate on the expansion of the volume of liquid in the bulb.
As this volume expands it forces the liquid up into the glass
tube.

Calibrating or creating a temperature scale with 0-degrees for
the ice point of water and with 100-degrees for the
steam point of water (both at 1 atm pressure) is the basis
of the Celsius scale. In the past, this was also known as
the centigrade scale.

In the United States, it is still common to use the Fahrenheit
scale. On the Fahrenheit scale, water freezes at 32oF
(0oC) and water boils at 212oF
(100oC). There are interesting stories as to how
Fahrenheit may have devised his thermometer scale. It, too, may
have been a "centigrade" scale with 0oF the lowest
temperature Fahrenheit could obtain with water, ice, and
salt and 100oF his not-quite-right measure of
human body temperature.

Conversion from Celsius to Fahrenheit

[ It is sometimes helpful to distinguish between an
actual temperature, such as 100oC, and a temperature
difference, such as 15 Co, by using oC for
the actual temperature and Co for the
temperature difference. While this is no "big deal", it is
sometimes helpful. ]

100 Co = 180 Fo

1 Co =
(9/5)
Fo

1 Fo =
(5/9)
Co

TC =
(5/9)
(TF - 32)

TF =
(9/5)
TC + 32

Listening to an international news segment on CNN, you hear
that the local temperature is 42oC. What is that on the
Fahrenheit temperature scale?